Evolution and Diversity of Life

Concepts and Sections to study

Note: We have covered the section on Darwin’s theory pretty well already. That

part will be a review.

Concepts to know• All of Chapter 14 • Chapter15

– Gene Pool– Gene Flow– Genetic drift– Population Bottleneck– Founder effect– Endangered species– Extinction

• Chapter 16– What is a species?– Premating, prezygotic, post mating and post zygotic reproductive

isolation– Allopatric and Sympatric speciation

• Chapter 17– Only section 17.1 and 17.2

Omit these

• Hardy Weinberg Principle

• Page 309-310

• Page 327

• Section 17.3 to 17.6

14.1 How Did Evolutionary Thought Evolve?

• 14.1.1 Early Biological Thought Did Not Include the Concept of Evolution

• 14.1.2 Exploration of New Lands Revealed a Staggering Diversity of Life

• 14.1.3 Fossil Discoveries Showed That Life Had Changed Over Time

– Figure 14.1 The Grand Canyon of the Colorado River (p. 266)

– Figure 14.2 Types of fossils (p. 266)

– Figure 14.3 Fossils of extinct organisms (p. 267)

eggs in nest fossilized feces (coprolites)

bones footprints skin impression

Darwinism• Darwin’s theory by Natural Selection

– Accepted theory by science– Called Darwinism or Darwinian Evolution

Large ground finch, beaksuited to large seeds

Small ground finch, beaksuited to small seeds

Warbler finch, beaksuited to insects

Vegetarian tree finch, beaksuited to leaves

Results of artificial selectionA clue for DarwinBreeder can select for desired charactersDepends upon natural variation

Darwin had a lot of help!• Darwin had a lot of help!

– Lamarck – proposed theory of evolution but had one fatal mistake in his theory (inheritance of acquired characteristics)

– Malthus (economist) – population increases, competition for resources results in struggle for survival

– Darwin (naturalist) – Went on a Voyage, studied many organisms (especially finches in Galapagos islands) and with the existing theories of Lamarck and Malthus put forward the theory of natural selection

– Wallace -Naturalist who arrived at the same conclusions Darwin did, encouraged Darwin to publish his work.

*

Natural Selection• Individuals that make up a population are not all identical

(variability) • this variation can be inherited (Heritable Variation in the

population) • Organisms have the potential to increase in numbers

greatly in excess of the ability of their    environment to support them (limits on reproductive success)

• Variation leads to differential rates in survival and reproductive success among the variations. Therefore those individuals with inheritable traits that increase their chances of successful reproduction will leave more offspring.  (natural selection)

• Differential survival and reproduction leads to a shift in the frequency of characters.  If this process goes on long enough, parent and daughter species can no longer interbreed, and there results a new species.

Genetic Variation• Heritable differences among individuals• Raw material of evolution

Adaptive Traits• Allow individuals to live to reproduce

• Provides opportunity for future change

Mutations

• Permanent change in genetic variation

• Only source of new alleles

• Do not arise out of need

• Causes of mutation– Spontaneous occurrence– Radiation– Chemicals– Transposons

Relatively constant resourcesand population size over time

Potential forrapid reproduction

Competition for survivaland reproduction

Variability instructures and behaviors

NATURAL SELECTION:On the average, the fittest

organisms leave the most offspring

Some variabilityis inherited

EVOLUTION:The genetic makeup of the population

changes over time,driven by natural selection

Observation

Conclusion based on observation

Results of Mutations

• Harmful– Nonadaptive– Eliminated by selection

• Beneficial – Adaptive– Selected and persist

• Neutral– Neither adaptive nor nonadaptive– May or may not persist in gene pool

Recombination

• Major source of genetic variation

• Three processes– Segregation– Independent assortment– Fertilization

Sickle Cell Mutation

• Single nucleotide mutation

• Cell sickle disease is recessive

• Heterozygous resistant to malaria– Not affected by disease– Confers advantage

dies of malaria lives andreproduces

dies ofsickle-cell anemia

dies of malaria lives andreproduces

dies ofsickle-cell anemia

HH

HhHH

Hh hh

hh

hhHhHH

Other Factors that Change Gene Frequency• Genetic Drift

• Gene Flow

• Nonrandom Mating

Genetic Drift

• Change in frequency due to chance

• Sampling error– Random selection of alleles– Error refers to different possibilities– Results in population change with time

Gene Pool and Gene Flow

• All the alleles in each population = gene pool

• Exchange of genes with neighboring populations– Immigration = movement in– Emigration = movement out

• High gene flow = stability

Founder Effect• Small population can

cause extreme genetic drift• Small gene pools allow for

rapid change• Example: polydactyly in

Pennsylvania Amish

Bottleneck• Significant portion of population dies• Remaining small population results• Genetic drift can cause rapid change• Example: Elephant seals

time

event causingbottleneck

resulting populationoriginal population

Endangered species

• Very few (from 10s to 1000s) may be around

• Could go very quicly to extinction• Gene pool is very limited • Low variation i.e. loss of genetic diversity• Very susceptible to diseases and other

problems• Human activities are a major cause (esp.

habitat destruction

Extinction

• Death of all members of a species

• Major factors leading to extinction– Localized distribution– Overspecialization– Reduced genetic variability– Habitat destruction

Nonrandom Mating• Types of nonrandom mating

– Inbreeding– Mate selection

• Reduces genetic variability

What is a Species?• No universal definition

• Species concepts– Morphological species concept– Biological species concept

16.1 What Is a Species?

• 16.1.1 Biologists Need a Clear Definition of Species

• 16.1.2 Species Are Groups of Interbreeding Populations

• 16.1.3 Appearance Can Be Misleading– Figure 16.1 Members of a species may differ

in appearance (p. 303)

How do new species develop?

• Ways species may achieve genetic isolation– Allopatric speciation– Sympatric speciation

Allopatric speciation Sympatric speciationtime

original population

geographical isolation

genetic divergence

reproductive isolation reproductive isolation

genetic divergence

ecological isolation

original population

Allopatric Speciation

• Populations living in different locations

• Physical barrier blocks gene flow

• Populations evolve differently

• If brought back together, populations will not interbreed

Continental Drift

• Movement of continents over time

• Continue to move slowly

• Movement has separated populations

• Example family of flightless birds (ratites)

Sympatric Speciation• Speciation within the same area

• Isolated by different ecological zones

• Most important in plant evolution

Origin of the Universe

• Big Bang– Explosion of super-condensed matter– Approximately 15 billion years ago

Origin of Earth• Early stars exploded forming nebulae

• Space debris gave rise to stars & planets

• Solar system formed 4.6 billion years ago

Earth’s Organic Molecules

• ~3.8 billion years ago– Cooling earth– Volcanoes – Conditions to form complex organic molecules

Could Organic Molecules Spontaneously Form?

• Stanley Miller & Harold Urey– Tested hypothesis– Created closed glass vessel– Introduced gasses

• Methane• Ammonia • Water vapor • Hydrogen gas

– Electrodes stimulated lightning

Results of Experiment

• Within a week complex molecules formed– Amino acids– Nucleic acids– Fatty acids

• Primordial soup Theory

Another Possibility

• Life may have arisen in hydrothermal vents– Energy & nutrients exist

• Hot gasses• Sulfur compounds

Biological Evolution

• May have started with self-replicating RNA– RNA can carry information just like DNA– RNA can also carry out enzymatic reactions

like proteins– Suggestion that there may have been a

primitive “RNA world”

• RNA enclosed in membrane• Enzymes could be organized• Still no scientific consensus of these points

First Cells

• About 3.5 billion years old

• Pigment system 2.5 to 3.3 billion years ago– Cyanobacteria– Allowed for oxygen production

Eukaryotic Cells

• Appeared about 2.1 bya

• Began to diversify 1 – 1.2 bya– After evolution of sexual reproduction– Sufficient oxygen levels

Serial Endosymbiotic Theory

• Proposed by Lynn Margulis

• Prokaryotes engulfed other prokaryotes

• Engulfed prokaryotes escaped digestion

• Endosymbionts benefited from protection

• Precursors to mitochondria

Rise of Multicellular Organisms

• Earliest algae – 1.2 bya

• Multicellular animals – 600 mya

• Explosion of life in Cambrian period